The only pitch gear you should run would be 48 pitch. 64 is for touring, and 32 is for nitro applications (And Tamiya newbie proof cars).
Just be careful that with the different gearing you still have room to move the motor back.
So why are you 7 oz. overweight?
Ever think about such things like milling out some aluminum? Get rid of steel turnbuckles and replace them with other turnbuckles. Also, try finding an aluminum screw kit with everything you need to convert the truck. The weight will be trivial at best, but it is something.